1. Field of the Invention
The present invention relates to high-frequency switch modules and high-frequency switch apparatuses, and more particularly, to high-frequency switch modules and high-frequency switch apparatuses used in wireless communication apparatuses which can be used in a plurality of different communications systems.
2. Description of the Related Art
Examples of mobile communications systems include GSM 900 (Global System for Mobile Communications 900), GSM 1800 (Global System for Mobile Communications 1800) widely used in Europe, GSM 850 (Global System for Mobile Communications 850) widely used in North America, and PDC (Personal Digital Cellular) system widely used in Japan. Examples of CDMA systems used in parallel with GSM include CDMAOne (Code Division Multiple Access One) and IMT-2000 (International Mobile Telecommunications 200). Recent widespread use of mobile phones has caused a problem in that frequency bands assigned to each of the mobile communications systems are not sufficient for providing services to all of the users of the systems, resulting in interruptions of communications or difficulties in making connections particularly in large city areas. Thus, it has been proposed to allow a user to use a plurality of mobile communications systems thereby substantially increasing the available frequencies, improving service, and enabling efficient use of infrastructures.
Accordingly, an antenna switch circuit disclosed in Japanese Unexamined Patent Application Publication No. 2004-253953 has been disclosed. The antenna switch circuit includes an antenna and a switch circuit. The antenna transmits and receives transmission and reception signals in a plurality of frequency bands. The switch circuit switches transfer paths so as to correctly output the reception signals in a plurality of frequency bands input from the antenna to the corresponding receiver circuits, as well as switches the transfer paths so as to correctly output the transmission signals to the antenna. Such a switch circuit includes a plurality of FET transistors, and the FET transistors, which are switched ON or OFF by control signals, switch transfer paths. The above-described antenna switch circuit enables transmission and reception signals in a plurality of types of frequency band to be handled in mobile phones.
In such an antenna switch circuit, it is necessary to prevent noise generated in a printed circuit substrate on which the antenna switch circuit is mounted from being input to the switch circuit of the antenna switch circuit. Accordingly, a capacitor, one end of which is grounded, is connected to the path through which a signal for controlling the switch circuit is transferred. This enables the noise generated in the printed circuit substrate to be transferred to the ground through the capacitor via a ground electrode within the printed circuit substrate, whereby the noise is prevented from being input to the switch circuit.
However, the above described antenna switch circuit still has a problem in that the high-frequency characteristics of the switch circuit are deteriorated due to noise, as will be described below. FIG. 5 is a cross-sectional view of an antenna switch circuit 100 and a printed circuit substrate 102 on which the antenna switch circuit 100 is mounted. The printed circuit substrate 102 includes the antenna switch circuit 100 and a capacitor 104 mounted thereon. The capacitor 104 is grounded through a ground electrode 106 provided within the printed circuit substrate 102 (it is not illustrated how the ground electrode 106 is grounded). The antenna switch circuit 100 is also grounded through the ground electrode 106.
In the antenna switch circuit 100, noise is also generated in the switch circuit (not illustrated) of the antenna switch circuit 100, in addition to the noise generated in the printed circuit substrate 102. These kinds of noise are transferred to the ground side through the capacitor 104 and the ground electrode 106 within the printed circuit substrate 102. However, as illustrated by an arrow in FIG. 5, a portion of the noise is input to the antenna switch circuit 100 through the ground electrode 106 when the antenna switch circuit 100 is connected to the ground electrode 106. Due to this, the noise is also input to the switch circuit of the antenna switch circuit 100, whereby a transmission signal is modulated by the noise. As a result, the harmonics of the transmission signal are distorted and thereby the high-frequency characteristics of the switch circuit are deteriorated.